A laser radar device measures a distance from the laser radar device to a subject that is located at a position outside of the laser radar device, by using a time interval from a time point that a laser light is emitted to a time point that the laser light is received. When the laser radar device measures the distance from the laser radar device to the subject, it is necessary to consider a delay time that is generated in a calculation operation such as a transmission time of a signal transmitted to a light emitting unit that emits the laser light, or a transmission time of a signal transmitted from the light emitting unit. The delay time dynamically varies when being affected by a temperature characteristic. Thus, the laser radar device measures a variation of the delay time when measuring the distance from the laser radar device to the subject, and corrects a formula used to calculate the distance based on the variation of the delay time.
According to JP2010-203820A, the laser radar device emits the laser light generated by a laser diode in a travelling direction deflected by a rotation mirror. Further, since a window that is a light transmitting plate is not arranged on an entire of a case in a peripheral direction, the laser light may travel in a direction toward the case.
According to JP2010-203820A, when the laser light travels in the direction toward the case, a reflection member that reflects the laser light is provided in the case. In this case, the laser radar device measures a sensing time from a time point that the laser light is emitted to a time point that a reflection light that is the laser light reflected by the reflection member is sensed. Since a length of a light path of the reflection light generated by the reflection member is known, a variation of the sensing time is correlative to the variation of the delay time. Thus, the laser radar device corrects the formula used to calculate the distance based on the sensing time of the reflection light.